<?php
/**
 * Created by PhpStorm.
 * User: Shen
 * Date: 2016/7/10
 * Time: 22:35
 */

class Db{
    static private $_instance;
    private function __construct(){

    }

    static public function getInstance(){
        if (!(self::$_instance instanceof self)){
            self::$_instance = new self();
        }
        return self::$_instance;
    }
}